256 OCTOBER TERM, 1907. Opimon of the Court. ?9 U.S. Foreseeing cases where national and state legislation based upon different powers might, in their application, be brought into conflict, he, in the same case (p. 211), declared tha? then "the law of the State, though enacted in the exercise of powers not controvcrtcd, must yield," a rnle which has constantly been applied by this court. These general principles control the decision of. the case at bar. Cattle, while in the course of transportation from one State to another, and in that respect under the exclusive control of the law of the National Govern- ment, may at the same time be the conveyance by which dis? ease is brought within the State to which they are destined, and in that respect subject to the power of the State exercised in good faith to protect the health of its own animals and its own people. In the execution of that power the State may enact laws for the. inspection of animals coming from other States with the purpose of excluding those which are diseased and admitting those which are healthy. ? v. Colorado, 187 U.S. 137. The State may not, however, for this purpose exclude all afiimals, whether diseased or not, coming from other States, Railroad v. Husen, 95 U.S. 465, nor under the pretense of pro- teeting the public health, employ inspection laws to exclude from its borders the products or merchandise of other States; and this court will assume the duty of determining for itself whether the statute before it is a genuine exercise of an acknowl- edged state power, or whether, on the other hand, under the guise of an inspection law it is really and substantially a regu- lation of foreign or interstate commerce which the Constitution has conferred exclusively upon the Congress. Minnesota v. Barber, 136 U.S. 313; Brimmerv. Rebman, 138 U.S. 78; Patap- sco Guano Co. v. North Carolina, 171 U.S. 345. Tested by these principles, the statute before us is an inspection law and nothing else, it excludes only cattle found to be diseased, and in the absence of controlling legislation by Congress it is clearly within the authority of the State, even though it may have an inci- dental and indirect effect upon commerce between the States.
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